1. Field of the Invention
The present invention relates to an antifoaming agent for use in fermentation processes, a fermentation medium which incorporates the antifoaming agent, a method of producing L-amino acids in the presence of the agent, and a method of defoaming using the agent.
2. Description of the Background Art
In the fermentative production of useful substances by submerged aerobic culture, a great number of bubbles and foam occur causing various problems. For example, when a fermenter becomes filled with bubbles the culture capacity per unit volume is lowered, and the culture solution can overflow.
Attempts to suppress such bubbling have included the addition of an antifoaming agent to the fermentation medium Polyoxyalkylene polyhydric alcohol ethers, polyoxyalkylene alkyl ethers, polyoxyalkylene fatty acid esters, polyoxyalkylene alkyl ether fatty acid esters, etc. are antifoaming agents previously used (Japanese Patent Application Laid-Open Nos. 4282/1975, 121482/1975, 135298/1979, 169583/1981 and 35073/1990). These antifoaming agents for fermentation baths have not proven very satisfactory, however, due to an unacceptable antifoaming effect, an adverse affect on fermentative production (inhibition of growth of microorganisms, inhibition of formation of products, etc.), a long incubation time before developing an antifoaming effect, or the inability to retain an antifoaming effect over long periods of time.
Since the fermentative production of L-amino acids such as L-glutamic acid, L-lysine, L-glutamine, L-arginine, L-phenylalanine, L-threonine, L-isoleucine, L-histidine, L-proline, L-valine, L-serine, L-ornithine, L-citrulline, L-tyrosine, L-tryptophan and L-leucine is commercially important, is carried out on an industrial scale by the fermentation of microorganisms belonging to Brevibacterium, Corynebacterium, Microbacterium, Bacillus, Escherichia or the like and encounters problems due to foam and bubbles, it is desirable to provide an antifoaming agent that overcomes the above drawbacks.
Further, conventional L-amino acid fermentation processes are unsatisfactory with respect to yield. In order to increase the yield, specific surfactants have been added to the fermentation medium so as to allow for continuous fermentation while crystallizing out the L-amino acid product (Japanese Patent Application Laid-Open No. 288/1977). However, this process has proven unsatisfactory with respect to overall yield, although improvement as compared with conventionally-known processes is obtained.